1. Field of the Invention
The present invention relates to a developing apparatus which is used in an electrophotographic apparatus. Particularly, the invention relates to a developing apparatus in which a developing roller carrying a single component toner is contacted with a photoreceptor drum carrying an electrostatic latent image to develop the electrostatic latent image with toner.
2. Description of the Related Art
In developing apparatuses using a single component but not any carrier, miniaturization can be achieved inexpensively and maintenance cost is low since their structure is relatively simple. Particularly, in the case of using no magnetic toner, an inexpensive small-sized apparatus that develops a clear picture can be put into practice because no magnetic roller is necessitated. The developing apparatuses using a non-magnetic single component toner can be classified roughly into two types. In one apparatus of a non-contact type, a photoreceptor drum carrying an electrostatic latent image is placed at the opposite side of a developing roller carrying toner without contact, in which an alternating current electric field is applied between them for the toner to flit reciprocally to develop an image. In another, contact type apparatus, the photoreceptor drum is contacted with and placed at the opposite side of a developing roller comprising a conductive elastic material, to which voltage is applied to develop an image. In the apparatus of non-contact type, developing bias voltage in which an AC voltage is mainly superimposed on a DC voltage is used, and in that of contact type, DC developing bias voltage is used.
For example, in Japanese Unexamined Patent Publication JP-A 3-87759 (1991) which discloses a developing method of the contact type in the prior art, necessity of difference in the relative velocity between the photoreceptor drum and the developing roller required for highly precise development, resistance value of the toner, and resistance value of the developing roller are disclosed. Moreover, in Japanese Examined Patent Publication JP-B2 63-26386 (1988) which discloses a developing method of the contact type of the prior art, a method for removing the electric charge of toner remaining in the roller by a conductive member contacting with the developing roller after completion of the development is disclosed. Furthermore, in Japanese Examined Patent Publication JP-B2 6-52448 (1994) which discloses a developing method of the contact type of the prior art is defined the relationship between coefficient of internal friction in a developing apparatus provided with a blade for regulating the toner on the developing roller in thickness, coefficient of friction of the toner with the developing roller, and coefficient of friction of the toner with the blade. Furthermore, Japanese Examined Patent Publication JP-B2 63-26391 (1988) discloses an apparatus for electrostatically or mechanically removing toner adhered to a part other than an image part by applying a voltage of the same polarity as that of the toner to the conductive member a developing apparatus in which a developing apparatus including a developing roller, a conductive member and transfer apparatus are sequentially disposed around the photoreceptor drum along with a rotating direction of the photoreceptor drum.
The conditions disclosed in the JP-A 3-87759 (1991) and JP-B2 6-52448 (1994) are insufficient for highly precise development since removal of the electric charge of toner remaining in the developing roller after completion of the development has not been considered. Moreover, in JP-B2 63-26386 (1988), the electric charge of toner remaining in the developing roller after completion of the development is removed by using a conductive member, but mere contact of the conductive member with the developing roller is accompanied by a fall, accumulation and scattering of the toner to make the inside of the apparatus dirty to probably soil copy sheets. Further, there is no detail description of conditions for the development, and so highly precise development is desired. Further, JP-B2 63-26391 (1988) relates to removal of the toner excessively adhered to the photoreceptor drum but not to the toner adhered on the developing roller.